f'(x)=3ax^2+2bx+c=0的两根为1,3故两根和=1+3=4=-2b/(3a),得:b=-6a两根积=3=c/(3a),得c=3a故f(x)=ax^3-6ax^2+3ax+12代入(2,4):8a-24a+6a+12=4,得:a=0.8因此f(x)=0.8x^3-4.8x^2+2.4x+12,5,已知函数f(x)=ax^3+bx^2+cx+12有极值点x=1,x=3,曲线y=f(x)的拐点(2,4),求a,b,c的值,并写出曲限方程